The present invention relates to a testing arrangement for non-destructive testing of ferro-magnetic bodies for structural defects by means of magnetizing the bodies in which the structural defects cause changes in the magnetic field pattern, the changes being picked up by stationary magnetic field detectors arranged on or near the surface of the bodies, the detectors being arranged along the periphery of the bodies and having outputs connected in a specified sequence and in a time-division multiplex manner to an evaluation circuit.
In the prior art, when welded pipes of ferritic material are tested, the lines of weld cause stray fluxes which limit the error tracing capability of systems with rotating magnetic fields. In the case of lines of weld extending in the longitudinal direction of the pipe, the magnetic field probes are arranged in differential connection. The magnetic field probes also extend along the longitudinal axis of the pipe. The measured values outputted by the magnetic field probes are weighted differently because of the lines of weld. A disadvantage here, however, is that long longitudinal errors can only be recognized in the entrance and exit area of the testing arrangement.